Photovoltaic element module and its production method, and non-contact treatment method

ABSTRACT

Before electrically connecting at least two photovoltaic elements, a medium capable of absorbing at least 10% or more of a light having a wavelength of 0.4 μm to 2.0 μm is provided on an electric connection portion of the photovoltaic element, whereby the present invention provides a method of electrically connecting a group of photovoltaic elements to one another with a high yield and easy automatization.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a photovoltaic element module and itsproduction method, and a non-contact treatment method, and morespecifically to a photovoltaic element module comprising a plurality ofelectrically connected photovoltaic elements and a method of producingthis module.

2. Related Background Art

The problem of the escalating global warming caused by the greenhouseeffect, that is, an increase in the amount CO₂ in the atmosphere, hasproduced a growing demand for the development of a clean energy sourcethat does not discharge CO₂. One of such energy sources is nuclearpower. Nuclear power, however, has many problems, such as radioactivewastes, so a safer clean energy source is desired. Of the expected cleanenergy sources, solar cells (photovoltaic elements) are gathering muchattention due to their cleanness, safety, and easy handling.

At present, the solar cells are roughly classified into a crystal typeusing single-crystal or polycrystal silicon, an amorphous type usingamorphous silicon, and a compound semiconductor type. Of these solarcells, the amorphous type is highly expected. That is, despite itsconversion efficiency being lower than that of the crystal type solarcell, the amorphous silicon solar cell has excellent characteristicsthat are absent from the crystal type solar cell. For example, it canoperate in the form of a film because the area of the amorphous typesolar cell can be easily increased. Also, it has a large photoabsorptioncoefficient.

One of the reasons for a slow dissemination of solar cells, despite theattention they have drawn, is their high cost. Various methods have beenexamined to reduce the production costs of solar cells. Therepresentative approaches include:

(1) Reduction of the production costs of a photoelectric conversionlayer,

(2) Efficient utilization of an electric power generating region,

(3) Reduction of the number of connections, reducing connection materialand labor costs, and

(4) Reduction of the use amount of covering materials and the materialcosts. Of these approaches, the present invention particularly relatesto the above point (3). The solar cell connection step is complicatedand requires high reliability. However, for simplification and costreduction, as well as the reduction of the number of parts, an automatedmass-production connection method and high speed treatment are required.

FIGS. 11A and 11B are schematic views showing an example of aphotovoltaic element which is disclosed in, for example, Japanese PatentApplication Laid-Open No. 8-139349 and which has been investigated bythe inventors. FIG. 11A is a plan view of the photovoltaic element asseen from its light-receiving surface side, and FIG. 11B is a sectionalview of the photovoltaic element shown in FIG. 11A, which is taken alongthe line 11B—11B in FIG. 11A.

A photovoltaic element 600 shown in FIG. 11, is produced by sequentiallystacking a lower electrode layer 603, a semiconductor layer 604, and anupper electrode layer 605 on a conductive substrate 602 of, for example,stainless steel.

The upper electrode layer 605 comprises a transparent conductive filmsuch as of indium oxide or indium tin oxide (ITO) and operates as both areflection-preventing means and a current-collecting means.

A part of the transparent conductive film is linearly removed at aportion as shown by 601 (an etching line) in FIG. 11A by using screenprinting or other methods of applying etching paste containing FeCl₃ orAlCl₃ to the film and heating it. A part of the transparent electrodefilm is removed in order to prevent a short circuit from occurringbetween the substrate 602 and the upper electrode layer 605 when theouter circumference of the photovoltaic element is cut.

In addition, a current-collecting electrode 606 is formed on the surfaceof the upper electrode layer 605 to efficiently collect generated power.The current-collecting electrode 606 is formed by adhering a metal wirecoated with the thin layer of a conductive adhesive (for example, acopper wire coated with a carbon paste) to the upper electrode layer 605in order to obtain electric power generated in the semiconductor layerwithout loss. The copper wire is used in order to reduce power loss, andmay be replaced by another highly conductive material.

Furthermore, a conductive foil 607 is provided as a furthercurrent-collecting electrode in addition to the current-collectingelectrode 606. An insulating member 608 is provided under the conductivefoil 607 to ensure the insulation provided by the etching line portion,the performance of which cannot be guaranteed.

In the photovoltaic element 600, the metal foil 607 and the substrate602 function, respectively, as terminals of a positive and a negativeelectrodes to provide electric power.

It is difficult, however, for this photovoltaic element to be directlyused for electric power generation. Since the single photovoltaicelement normally generates excessively low power, a plurality ofphotovoltaic elements must be connected in series or parallel to providea desired voltage and current. FIG. 11C is a plan view showing anexample of series-connected photovoltaic elements (in the case of twoseries). In this figure, the conductive foil 607 of one photovoltaicelement is electrically connected in series to the substrate 602 ofanother adjacent photovoltaic element by using a connection member 611.Solder is used for the connection and the series connection is completedby carrying out cleaning with a solvent such as MEK (methylethylketone)after soldering.

The conventional method of connecting photovoltaic elements to eachother, however, has the following problems.

(1) To fix the conductive foil to the metal substrate by using solder, apart of the substrate must be heated to melt and fix the solder. Theheat, however, is transferred through the thermally conductive metalsubstrate and the semiconductor layer may degrade over a wide areaworsening specific characteristics. In addition, defects may occur inthe semiconductor layer depending on the heating temperature or time,thereby reducing the yield.

(2) The heat for melting and fixing the solder may degrade theconductive adhesive provided on the semiconductor element to reduce theadhesion strength and electric conductivity, thereby reducingreliability.

(3) Since the solder must be melted, at least about ten seconds arerequired to heat and cool it, thereby negatively affectingmass-productivity.

(4) If an automatic machine is used for mass production, it is difficultto control the temperature to achieve uniform soldering and to controlthe tip of a soldering iron. Thus, automation is difficult.

(5) Even when the solvent, such as MEK, is used to wipe off the excesssolder, fluxes adhering to the substrate cannot be easily removed tocause rust under high-temperature and high-humidity conditions.Consequently, the covering material of the solar cell may be peeled off.

(6) Using a soldering iron for connections may produce solder residue toreduce the yield. For example, the solder residue may penetrate betweenthe adjacent photovoltaic elements connected in series to cause a shortcircuit therebetween.

On the other hand, the non-contact treatment method utilizing radiationof laser light, halogen light or electromagnetic waves is widely used inthe processing treatment for materials, such as etching, welding orcutting, or in thermal treatment for semiconductor materials. Such amethod can more or less solve the problems of the connections usingsolder.

It is important for the non-contact treatment, however, to efficientlyabsorb light, heat, or electromagnetic waves. When, for example, amaterial such as gold, silver, copper, or aluminum is used which arefrequently used for electrodes for electric parts, in particular,photovoltaic elements, these materials have a high surface reflectancewith respect to the laser light and therefore exhibit a lower efficiencyof absorbing energy. Thus, the idea for improving the absorptionefficiency of energy is required. Also, a method of improving theabsorption efficiency of energy is required that can increase theefficiency of energy absorption without the need for additional stepsand that enables stable and high speed treatment.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve the above problems inorder to provide a photovoltaic element connection method that isreliable and easy to automate.

It is another object of the present invention to provide a photovoltaicelement connection method and a laser treatment method that enablesstable and high speed treatment and that utilizes an energy-absorbingmedium, and after treatment, the medium does not remain on the treatedsurface.

The present invention solves the above problems to achieve the aboveobjects. The present invention provides a photovoltaic element modulecomprising at least two photovoltaic elements electrically connected toeach other, wherein a medium capable of absorbing at least 10% or moreof a light having a wavelength of 0.4 μm to 2.0 μm is provided on anelectric connection portion of the photovoltaic element.

In addition, the present invention provides a method of producing aphotovoltaic module, which comprises electrically connecting at leasttwo photovoltaic elements to each other, wherein a medium capable ofabsorbing at least 10% or more of a light having a wavelength of 0.4 μmto 2.0 μm is provided on a part of a first photovoltaic element, andthen irradiating the medium with the laser beam at a wavelength of 0.4μm to 2.0 μm to electrically connect the first and second photovoltaicelements to each other.

Furthermore, the present invention provides a method of producing aphotovoltaic module, which comprises electrically connecting at leasttwo photovoltaic elements to each other, wherein each of thephotovoltaic element has at least a conductive substrate, asemiconductor layer, and a light-transmissive electrode, and whereinelectrically connecting the conductive substrate of a first photovoltaicelement and the light-transmissive electrode of a second photovoltaicelement to each other is done by laser welding.

Moreover, the present invention provides a non-contact treatment methodof carrying out treatment by using an energy supply means for applyingenergy, which comprises placing a non-adhering medium capable ofabsorbing the energy on a material to be treated and irradiating thenon-adhering medium with energy.

Moreover, the present invention provides a method of producing aphotovoltaic module, which comprises electrically connecting at leasttwo photovoltaic elements to each other, wherein a non-adhering mediumcapable of absorbing the energy is placed on a part of a firstphotovoltaic element and the medium is irradiated with energy toelectrically connect the first photovoltaic element and a secondphotovoltaic element to each other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic views showing an appearance of aphotovoltaic element module according to Example 1 of the presentinvention. FIG. 1A is a plan view of the photovoltaic element as seenfrom its light-receiving surface side, and FIG. 1B is a sectional viewof the photovoltaic element shown in FIG. 1A, which is taken along theline 1B—1B in FIG. 1A;

FIG. 2A is a plan view of two series-connected photovoltaic elements,each of which is shown in FIGS. 1A and 1B, as seen from theirlight-receiving surface side.

FIG. 2B is an enlarged view of the series-connected portion in FIG. 2A,and

FIG. 2C is a sectional view of the portion as shown in FIG. 2B;

FIGS. 3A and 3B are schematic views showing an appearance of aphotovoltaic element module according to Example 2 of the presentinvention. FIG. 3A is a plan view of the photovoltaic element as seenfrom its light-receiving surface side, and FIG. 3B is a sectional viewof the photovoltaic element shown in FIG. 3A, which is taken along theline 3B—3B in FIG. 3A;

FIG. 4A is a plan view of two series-connected photovoltaic elements,each of which is shown in FIGS. 3A and 3B, as seen from theirlight-receiving surface side.

FIG. 4B is an enlarged view of the series-connected portion in FIG. 4A,and

FIG. 4C is a sectional view of the portion shown in FIG. 4B;

FIGS. 5A and 5B are schematic views showing an appearance of aphotovoltaic element module according to Example 3 of the presentinvention. FIG. 5A is a plan view of the photovoltaic element as seenfrom its light-receiving surface side, and FIG. 5B is a sectional viewof the photovoltaic element shown in FIG. 5A, which is taken along theline 5B—5B in FIG. 5A;

FIG. 6A is a plan view of two series-connected photovoltaic elements,each of which is shown in FIGS. 5A and 5B, as seen from theirlight-receiving surface side.

FIG. 6B is an enlarged view of the series-connected portion in FIG. 6A,and

FIG. 6C is a sectional view of the portion shown in FIG. 6B;

FIGS. 7A and 7B are schematic views showing an appearance of aphotovoltaic element module according to Example 4 of the presentinvention. FIG. 7A is a plan view of the photovoltaic element as seenfrom its light-receiving surface side, and FIG. 7B is a sectional viewof the photovoltaic element shown in FIG. 7A, which is taken along theline 7B—7B in FIG. 7A;

FIG. 8A is a plan view of two series-connected photovoltaic elements,each of which is shown in FIGS. 7A and 7B, as seen from theirlight-receiving surface side.

FIG. 8B is an enlarged view of the series-connected portion in FIG. 8A,and

FIG. 8C is a sectional view of the portion shown in FIG. 8B;

FIGS. 9A and 9B are schematic views showing an appearance of aphotovoltaic element module according to Example 5 of the presentinvention. FIG. 9A is a plan view of the photovoltaic element as seenfrom its light-receiving surface side, and FIG. 9B is a sectional viewof the photovoltaic element shown in FIG. 9A, which is taken along theline 9B—9B in FIG. 9A;

FIG. 10A is a plan view of two series-connected photovoltaic elements,each of which is shown in FIGS. 9A and 9B, as seen from theirlight-receiving surface side.

FIG. 10B is an enlarged view of the series-connected portion in FIG.10A, and FIG. 10C is a sectional view of the portion shown in FIG. 10B;

FIGS. 11A, 11B, and 11C are schematic views showing an appearance of aconventional photovoltaic element module. FIG. 11A is a plan view of thephotovoltaic element as seen from its light-receiving surface side, FIG.11B is a sectional view of the photovoltaic element shown in FIG. 11A,which is taken along the line 11B—11B in FIG. 11A, and FIG. 11C is aplan view of two series-connected photovoltaic elements as seen fromtheir light-receiving surface side;

FIG. 12 is a sectional view schematically showing a configuration of thephotovoltaic element;

FIG. 13 is a graph showing the reflective characteristics of metals;

FIG. 14 is a graph showing the relationship between thephotoabsorptivity of a medium and the welding stability;

FIG. 15 is a graph showing the welding stability of a light-absorbingmedium;

FIG. 16 is a graph showing the relationship between the thickness of afilm and the adhesive strength of the film after welding;

FIG. 17 is a schematic view showing a laser treatment method accordingto Example 6;

FIGS. 18A and 18B are schematic views showing an appearance of aphotovoltaic element module according to Example 7 of the presentinvention. FIG. 18A is a plan view of the photovoltaic element as seenfrom its light-receiving surface side, and FIG. 18B is a sectional viewof the photovoltaic element shown in FIG. 18A, which is taken along theline 18B—18B in FIG. 18A;

FIG. 19A is a plan view of two series-connected photovoltaic elements,each of which is shown in FIGS. 18A and 18B, as seen from theirlight-receiving surface side.

FIG. 19B is an enlarged view of the series-connected portion in FIG.19A, and

FIG. 19C is a sectional view of the portion shown in FIG. 19B;

FIG. 20 is a schematic view showing a method of supplying a non-contactmedium;

FIG. 21 is a graph showing the relationship between the mean squaresurface roughness of the non-contact medium and its welding reliability;and

FIG. 22 is a graph showing the relationship between the mean squaresurface roughness of the non-contact medium and its adhesion strength toa treated material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention are described below withreference to the drawings.

Photovoltaic Element

FIG. 12 schematically shows a sectional view of an example of aphotovoltaic element used in the present invention. In this figure,numeral 701 indicates a substrate, 702 a lower electrode layer, 703 asemiconductor layer, and 704 an upper electrode layer. The photovoltaicelement shown in FIG. 12 can be applied to an amorphous silicon typesolar cell, which is, preferably, flexible. Such a configuration,however, can be applied to solar cells other than the amorphous typesolar cells, such as a single crystalline or polycrystalline solar cell,or a solar cell using a semiconductor other than silicon or having theSchottky junction.

The substrate 701 is a member for mechanically supporting thesemiconductor layer 703 in a thin solar cell of amorphous silicon type.The material for the substrate 701 may be conductive or insulating butmust be conductive when the substrate 701 also acts as an electrode. Thesubstrate 701 must be durable enough to withstand the heatingtemperature for forming the semiconductor layer 703.

The conductive material for the substrate 701 includes metals such asFe, Ni, Cr, Al, Mo, Au, Nb, Ta, V, Ti, Pt, and Pb; and alloys thereof,for example, a sheet metal such as brass or stainless steel; andcomposites thereof.

The electrically insulating material for the substrate 701 includesheat-resistant synthetic resins, such as polyester, polyethylene,polycarbonate, cellulose acetate, polypropylene, polyvinyl chloride,polyvinylidene chloride, polystyrene, polyamide, polyimide, and epoxyresin; and their composites with glass, carbon, boron, or metal fibers;glass; and ceramics.

Lower Electrode Layer

The lower electrode layer 702 is one of the electrodes for collectingelectric power generated in the semiconductor layer 703 and mustfunction in such a way that the lower electrode layer 702 forms an ohmiccontact with a semiconductor.

The material for the lower electrode layer 702 includes metals such asAl, Ag, Pt, Au, Ni, Ti, Mo, Fe, V, Cr, Cu, stainless steel, brass,nichrome, SnO₂, In₂O₃, ZnO, and ITO (indium tin oxide); and alloysthereof; and transparent conductive oxide (TCO).

The surface of the lower electrode layer 702 is preferably smooth, butmay be textured when it irregularly reflects light. In addition, whenthe substrate 701 is conductive, the lower electrode layer 702 may beomitted.

The lower electrode layer 702 may be provided by a well-known method,such as plating, deposition, or sputtering.

Semiconductor Layer

The semiconductor layer 703 of the photovoltaic element used in thepresent invention comprises a well-known semiconductor materialgenerally used for thin film solar cells. Specifically, it is possibleto use as the semiconductor layer 703, a pin-junction amorphous siliconlayer, a pn-junction polycrystalline silicon layer, or a layer of acompound semiconductor such as CuInSe₂/CdS.

When the semiconductor layer 703 is an amorphous silicon layer, it canbe formed by introducing a raw material gas, such as silane gas forforming a film, into a plasma CVD apparatus for generating plasmadischarge. In addition, when the semiconductor layer 703 is apn-junction polycrystalline silicon layer, it can be formed by forming afilm using molten silicon. When the semiconductor layer 703 consists ofa compound semiconductor such as CuInSe₂/CdS, it can be formed by theelectron beam deposition method, the sputtering method, or theelectrodepositon method.

Upper Electrode Layer

The upper electrode layer 704 is one of the electrodes for collectingthe electromotive force generated in the semiconductor layer 703 and ispaired with the lower electrode layer 702. Like the lower electrodelayer 702, the upper electrode layer 704 must function in such a waythat the layer 704 forms an ohmic contact with a semiconductor. Theupper electrode layer 704 is required when the semiconductor layer 703comprises a semiconductor such as amorphous silicon having a high sheetresistance, and is not particularly required when a crystallinesemiconductor is used, due to its low sheet resistance.

When the substrate 701 is opaque, the upper electrode layer 704 isnecessarily located on the light incident side. In this case, the upperelectrode layer 704 must transmit light, that is, must be a transparentelectrode. To allow light from the sun or a white fluorescent lamp to beefficiently absorbed by the semiconductor layer 703, the lighttransmittance of the upper electrode layer 704 is preferably 85% ormore. In addition, to allow a photoelectric current generated in thesemiconductor layer 703 to efficiently flow in a direction parallel tothe semiconductor layer 703, the sheet resistance of the upper electrodelayer 704 is preferably 100 Ω/□ or less. The material having thesecharacteristics and preferred for the upper electrode layer includesmetal oxides such as SnO₂, In₂O₃, ZnO, CdO, CdSnO₄, and ITO(In₂O₃+SnO₂).

Non-contact Treatment and Method of Producing Photovoltaic ElementModule

The non-contact treatment according to the present invention can beapplied to welding or cutting of various parts, including electric partsor general structures formed of either a metal material or a nonmetalmaterial by energy irradiation, to etching or patterning during a stepof producing an electric-part, and to the thermal treatment ofsemiconductor materials.

In the present invention, laser welding is applied particularly tophotovoltaic elements. The energy supply means used in the presentinvention and the medium capable of absorbing energy are described belowand are the features of the photovoltaic element module according to thepresent invention.

Energy Supply Means

As the energy supply means according to the present invention, light,heat or electromagnetic waves can be suitably used. Heating byirradiation of light, such as laser light, a halogen lamp or a farinfrared lamp, can be used.

The laser used for laser welding according to the present inventionincludes a solid laser, such as ruby (Cr³⁺: Al₂O₃), YAG (Nd³⁺:Y₃Al₅O₁₂), phosphate glass, silicate glass, YLF (Nd³⁺: LiYF₄), orThailand sapphire (Ti³⁺: Al₂O₃), and a gas laser such asCO₂-laser-excited or discharge-excited far infrared radiation or raregas ions.

The metal material used for a system, such as a solar cell, which has alarge current flow, preferably has a low resistance in order to reducelosses caused by the resistance. As shown in FIG. 13, however, thereflectance is relatively high when the metal is irradiated with lighthaving a wavelength of 0.4 μm or more. Thus, it has been difficult toweld metal with laser light having a wavelength of 0.4 μm or more. Onthe other hand, the use of laser light of less than 0.4 μm increasescosts, for example, for excimer lasers. Accordingly, the use of laserlight having a wavelength of not more than 0.4 μm has been limited toexpensive high-value products.

The present invention allows the use of laser light having a wavelengthof 0.4 μm or more to weld metal.

Of the lasers having a wavelength of 0.4 μm or more, solid lasers (thewavelength of main solid lasers is in a range of 0.4 μm to 2.0 μm) aremore efficient than gas lasers and have the advantages of being morecompact and providing higher-power laser light. In particular, YAGlasers have excellent characteristics, such as their capabilities oftransmitting laser light through optical fibers and executing welding ata position remote from a laser transmitter. They also enable the weldingconditions to be changed by the selection of optical fibers and outgoingunits and also enable one laser beam to be divided into about 2 to about10 beams.

Medium Capable of Absorbing Energy

The reflectivity obtained when a metal is irradiated with light dependson the type of metal, and is shown in FIG. 13. Despite the amount ofreflection depending on the wavelength, most irradiation light isreflected particularly at the long wavelength side. For example, at 0.7μm, which is close to the wavelength of ruby laser beams (0.69 μm), thereflectances of gold, silver, copper, and aluminum are 97.0%, 98.5%,97.5%, and 89.8%, respectively. The reflectances at the YAG laserwavelength (1.06 μm) of gold, silver, copper, and aluminum are 98.2%,98.9%, 98.5%, and 93.9%, respectively. Thus, it has been difficult toweld metal such as gold, silver, copper, and aluminum used forphotovoltaic elements, by using the ruby or YAG laser.

Medium Capable of Absorbing at Least 10% or More of Laser Light HavingWavelength of 0.4 μm to 2.0 μm

Thus, in the present invention, a medium capable of absorbing 10% ormore of laser light is provided on a surface to be welded to reduceinappropriate welding while enabling stable laser welding. Inparticular, the medium preferably has an absorptivity of 10% or more at0.4 μm to 2.0 μm, which is in the wavelength range of the above solidlaser.

FIG. 14 shows the effects obtained by providing a medium capable ofabsorbing 10% or more of laser light on a surface to be welded.

FIG. 14 is a graph showing the relationship between thephotoabsorptivity of the medium and welding stability obtained when acopper foil and a silver-plated copper foil (each having a thickness of100 μm) having a high reflectance were selected as a metal to beirradiated with laser light and when paint was applied uniformly to thesurface of the metal as the medium, followed by the irradiation of YAGlaser beams (wavelength: 1.06 μm) to carry out welding. A plurality ofpaints having different photoabsorptivities were used for evaluations.In addition, welding was carried out under conditions optimal for eachreflectance (however, copper and silver-plated copper were welded underthe same conditions). Furthermore, in evaluating the welding stability,a sample after welding that exhibited a joining force of 4.0 kg or moreafter thermal cycle tests (200 cycles at 90° C. to −40° C.) and in whichno holes or cracks were found in the welded portion when observed usingan optical microscope, was regarded as a good product (non-defectiveproduct). Thus, all the obtained samples were evaluated based on thenon-defective percentage.

Since copper and silver reflect 98.0% or more of laser light having awavelength of 1.06 μm, the welding stability of the metal is normally40% or less. Thus, it is difficult to subject them to laser welding. Asshown in FIG. 14, however, by providing a medium capable of absorbinglight on the surface of the metal, it is possible to improve the weldingstability of the metal. In particular, the welding stability is 80% ormore when the medium has a photoabsorptivity of 10% or more.

The energy (welding energy) required for welding a metal by using laserlight can be represented by the following equation.

(Welding energy)=(laser outgoing energy)×(photoabsorptivity of metal)

Normally, when a metal is welded using laser light, laser light having alarger energy than the welding energy must be supplied in considerationof the surface reflection of the metal. If, for example, the metal has alight reflectance of 90%, it is necessary to irradiate the metal withlight having a laser outgoing energy which is 10 times as large as thatrequired for metal with no reflection. Once laser light is introducedinto the metal, the metal melts and readily absorbs laser light.Consequently, most of the energy supplied is used for welding. When,however, the metal is, for example, a thin foil used for a photovoltaicelement, excessive energy may increase the temperature of the irradiatedportion above the melting point of the metal, resulting in holes in themetal. In the present invention, a medium capable of absorbing laserlight having a wavelength of 0.4 μm to 2.0 μm is provided on the surfaceof a metal to be irradiated with laser light to restrain the reflectionfrom the surface of the metal and allow laser light to be easilyintroduced into the metal. For example, in the case of executing weldingthat requires 5J, 50J outgoing energy is required when the reflectanceof the metal is 90%, whereas it is possible to execute welding with 251outgoing energy when the reflectance of the surface can be reduced to80% by using a medium. That is, by providing a light-absorbing medium onthe surface of metal having high surface reflection, the outgoing energyof laser light can be considerably reduced. This configuration canprevent holes from being formed in the metal.

Although the above discussion mentions the use of paints as the mediumcapable of absorbing light, the medium according to the presentinvention is not limited to paints and may be appropriately selectedregardless of whether the materials are insulating or conducting. Theinsulating material used for the medium according to the presentinvention, however, must melt when heated during welding to maintain theconductivity between the metal members.

Specifically, the object of the present invention can be sufficientlyachieved by coloring the surface of the metal member using felt pen orink jet. The color is preferably other than white to provide a largerphotoabsorption coefficient. To improve the welding stability, an inkapplication method that enables ink to be uniformly applied ispreferably used. Various methods can be used, such as, for example, thehardening of a silk-screen-printed ink by using a hot air dryingfurnace.

In addition, instead of using an ink, a film material such as a blackPET polyethyleneterephthalate) film (for example, trade name: LUMIRRORX30, produced by Toray Industries, Inc.; and trade name: MELINEX 427,produced by ICI Japan Ltd.) may be stuck to the surface of the metalmember, and the metal member may be welded together with the film byirradiating it with laser light from the film side. After welding, thefilm is preferably removed, but may not be removed depending on thematerial of the film. When the thickness of the film is in a range of 5μm to 30 μm, welding is stabilized to allow the film to be removedeasily after welding.

Furthermore, when a conductive material is used as the medium, a metalmaterial of a large photoabsorption coefficient may be selectively used.Specifically, an iron based material, such as stainless steel, amaterial plated with Ni or solder, a material obtained by treating in astrong-acid solution to oxidize or etch the surface of a metal, amaterial coated with carbon black, or a material with conductive fineparticles dispersed therein may be located on the surface of the metalmember, which is then welded together with the conductive material.After welding, the conductive material is preferably removed, but maynot be removed depending on the material.

The metal member may be plated with Ni or solder to use the Ni or solderas the medium capable of absorbing light.

FIG. 15 shows examples of welding stability, which were obtained whenthe above-mentioned media and YAG laser were used to carry out welding.The details of the media shown in FIG. 15 are as follows.

Felt pen:

Oily Magic Ink No. 500

Manual application

Photoabsorptivity: 10%

Silk screen printing:

Emerson & Cuming CT-5079-3A

(Produced by National Starch & Chemical Company)

Felt pen:

Oily Magic Ink No. 500

Printer

Photoabsorptivity: 60%

Ink jet printer:

JP-K27 (produced by Hitachi Manufacturing Company)

Dedicated printer

Photoabsorptivity: 25%

Black PET tape:

MELINEX 427 (produced by ICI Japan Ltd.)

(LUMIRROR X (Produced by Toray Industries, Inc.) or Black-TreatedLUMIRROR T (Produced by Toray Industries, Inc.)

Ni plating:

Photoabsorptivity: 60%

Thickness: 2 μm to 5 μm

Photoabsorptivity: 50%

Surface oxidation:

Electrolytic treatment

Photoabsorptivity: 20%

All the media provided satisfactory results, that is, their weldingstabilities were 70% or more.

Non-Adhering Medium

The following materials are applicable as the non-adhering mediumaccording to the present invention.

The applicable materials include paper; cloth; leather; thin metalfoils, such as stainless steel, steel and black alumite; polyesterfilms, such as a polyethyleneterephthalate film, apolybutylene-terephthalate film, a polyethylenenaphthalate film, apolycyclohexylenedimethyleneterephthalate film, and apolyethylenebisphenoxycarboxylate film; polyolefin films, such as apolyethylene film and a polypropylene film; a cellulose derivative film,such as a cellulose acetate butylate film and a cellulose acetatepropionate film; vinyl resin films, such as a polyvinyl chloride filmand a polyvinylidene chloride film; polymer films, such as a polystyrenefilm, a polyamide film, a polyimide film, a polycarbonate film, apolysulfone film, a polyurethane resin film, an epoxy resin film, and afluoride resin film; and a composite material comprising the abovepolymer film laminated with a thin metal foil, such as a stainlesssteel, foil, a steel foil, or a black alumite foil.

When the medium has at least the polymer film among the above materials,the polymer film is thin and strong and can be removed easily afterwelding because the polymer film melts and evaporates during energyirradiation. In addition, the polymer films supplied on the market arelong, so that high-volume welding can be carried out.

The objects of the present invention are best accomplished when themedium is a magnetic tape. This is because this material is excellent inworkability, mold-releasing capability, and high-speed treatment. Themold-releasing capability can be further improved by attaching themagnetic surface of the magnetic tape to a material to be treated.

Furthermore, the surface of the non-adhering medium that attaches to amaterial to be treated preferably has a surface roughness of 0.1 nm to5,000 nm. When the roughness is 5,000 nm or less, the non-adheringmedium efficiently guides, for example, laser light to the material tobe treated as shown in FIG. 21. When the surface of the non-adheringmedium that is attached to the material to be treated has a surfaceroughness of 0.1 nm or more in mean square, the non-adhering medium isunlikely to stick to the treated material during laser treatment asshown, for example, in FIG. 22. This allows the non-adhering medium tobe easily removed after laser treatment.

The methods of providing on at least a side of the medium that contactsthe material to be treated by energy irradiation, recessed andprotruding portions corresponding to a surface roughness of 0.1 to 5,000nm in mean square, include the use of the characteristics of thematerial itself in relation to the medium, the surface treatment byetching or discharge, the deformation of the surface shape by pressingor scratching, the mixing of a carbon block or a color material, such aspigment, into the polymer film, or the application or deposition of aselected material.

As one example of using the polyethylene-terephthalate film, theprotrusions on the surface of the polyethyleneterephthalate film can becontrolled by the selection of a polymerization medium for a raw polymermaterial or by adding inorganic particles to the film, as disclosed inJapanese Patent Publication No. 30-5639. More specifically, there is amethod of adding an oxide, such as SiO₂, TiO₂, CaCO₃, or Al₂O₃ or aninorganic salt, during the polymerization of the raw material polymer orduring the melting of pellets prior to drawing.

In addition, material that are applied or deposited onto the mediuminclude carbon black, graphite, titanium oxide, barium sulfate, zincsulfide, magnesium carbonate, calcium carbonate, zinc oxide, calciumoxide, magnesium oxide, tungsten disulfide, molybdenum disulfide, boronnitride, tin disulfide, silicon disulfide, chromium oxide, alumina,silicon carbide, cerium oxide, corundum, artificial diamond, iron oxide,garnet, silica rock, silicon nitride, molybdenum carbide, boron carbide,tungsten carbide, titanium carbide, diatomaceous earth, dolomite, alubricant such as a resin powder, an abrasive, an anti-static agent, adispersant, and a pigment. Also, dyes that may be combined with theabove materials can be used. For example, applicable dyes include aphthalocyanine dye, an azo dye, an anthraquinone dye, an indigoido dye,a nitro and nitroso dyes, a quinoline dye, a methyne dye, a thiazoledye, a quinoneimine dye, an azine dye, an oxazine dye, an thiazine dye,an azoic dye, a diphenylmethane dye, a triphenylmethane dye, a xanthenedye, acridine dye, an oxidation dye, a sulfidization dye, a phthaleindye, an aminoketone dye, or an oxyketone dye.

Paper, cloth, or a material coated with a pigment by a nozzle coater,such as carbon black, is preferably used as a non-adheringanti-reflection medium because “residue” resulting from heat duringlaser treatment is unlikely to stick to the treated material.

The means for supplying the non-adhering medium is not particularlylimited and may handle a sheet medium or a roll medium. However, themedium can be preferably attached and detached to such means and,preferably, continuously supplied to facilitate mass production.

When a sheet-like medium is supplied, it may have to be replaced at theend of each treatment or a means may be required for offsetting aposition so as to avoid irradiating the same position with energy. Thus,the medium is preferably supplied from the form of a roll and isdesirably wound up after treatment. When the medium is shaped like aroll, it can be continuously supplied by using a simple delivery andwinding mechanisms, thereby enabling mass production.

Material to be Treated

The material to be treated may be selected from various metal materialsor non-metal materials, and is not limited. The present invention,however, is particularly effective for a material having low absorptionwith respect to the energy used for treatment. Specifically, the presentinvention is effective for a high-reflection material reflecting atleast 40% or transmitting at least 40% of the energy used for treatment.

Specific metal materials that can be used include Fe, Ni, Cr, Al, Mo,Au, Nb, Ta, V, Ti, Pt, Pb, Ag, or Cu, or an alloy thereof, for example,stainless steel, brass, or nichrome. In particular, as a metal materialused for an electrode in an electric part through which a current flows,materials such as gold, silver, copper, or aluminum are preferably usedbecause they have low resistance, thereby reducing losses due toresistance. Laser light, however, is noticeably reflected from the abovemetals, as described above (FIG. 13). It has been difficult to directlyirradiate these metals with laser light having a wavelength of 0.4 μm ormore. Laser light having a wavelength of less than 0.4 μm requiresexpensive equipment, such as excimer lasers, and is unlikely to supplysufficiently amount of energy required for welding or cutting.Consequently, the application of such laser light has been limited.

In addition, as the non-metal material to be treated, it is possible touse a synthetic resin such as polyester, polyethylene, polycarbonate,cellulose acetate, polypropylene, polyvinyl chloride, polyvinylidenechloride, polystyrene, polyamide, polyimide, an epoxy resin, or afluororesin. Glass fibers, carbon fibers, or boron fibers, and glass orceramics may also be used.

Materials to be removed or the semiconductor materials to be thermallytreated by laser light during etching or patterning in the step ofproducing an electric part include single-crystalline silicon,polycrystalline silicon, amorphous silicon, a silicon-containingcompound, such as CuInSe₂/CdS, and SnO₂, In₂O₃, ZnO, or ITO (indium tinoxide).

The connection method according to the present invention has beenaccomplished by the inventors conducting experiments and detailedinvestigations in order to devise a method that is reliable and can beeasily automated to produce a photovoltaic element module byelectrically connecting at least two photovoltaic elements in series orin parallel. This method has the following effects.

(1) Since operations are completed faster than by conventionaltechniques and a welding point has the smallest area, the presentinvention has fewer portions adversely affected by heat. Thus, thepresent invention allows to achieve almost all specific characteristicsof the semiconductor. A further improvement may be accomplished byseparating a portion where welding is carried out by laser fromeffective areas via etching lines.

(2) In connecting photovoltaic elements, each comprising a semiconductorelement provided on the metal substrate, the metal substrate separatedfrom the effective areas via etching lines can be directly used as anoutput terminal electrode, thereby omitting the step of forming aterminal to reduce the non-electric power-generation area. This alsoapplies to conductive substrates other than metal substrates.

(3) In electrically connecting adjacent photovoltaic elements to eachother, a metal member is provided on the electrode portion of thesemiconductor element and the metal members of the photovoltaic elementsare electrically connected to each other by laser welding. Therefore,the semiconductor is almost not affected by the adverse effect of heat,thereby avoiding restrictions on the form of connection to enablearbitrary designs.

(4) A conductive adhesive can be used to join the semiconductor layerand collecting electrode of the photovoltaic element and to join thecollecting electrode of the photovoltaic element and the metal memberprovided on the electrode portion for simplification. In theconventional techniques using solder, heating for melting and fixingsolder causes the conductive adhesive to degrade, reducing the yield.The present invention, however, solves this problem, allowing theconductive adhesive to be used to produce a photovoltaic element module.

(5) When the metal members are welded together by laser light, the metalmaterial has reflective characteristics such as those shown in FIG. 13.Therefore, the energy of the laser light must be higher than is actuallyrequired for welding due to the surface reflection losses of the metal.However, once laser light is introduced into the metal, the metal meltsand readily absorbs laser light, thereby changing most of the suppliedenergy to welding energy. In this case, when the metal member is, forexample, a thin foil used for a thin photovoltaic element, an excessiveamount of energy raises the temperature of the portion irradiated withlaser light above the boiling point of the metal, causing holes to formin the metal member. In the present invention, a medium capable ofabsorbing 10% or more of laser light having a wavelength of 0.4 μm to2.0 μm is provided on the surface of the metal member to restrain thereflection from the surface of the metal member in order to allow laserlight to be easily introduced into the metal member. This configurationcan reduce the outgoing energy of the laser to simplify the welding ofmetal with a high surface reflectance, and stabilize the weldingstrength, thereby providing a reliable photovoltaic element module. Inaddition, the outgoing energy can be restricted to increase the lifetimeof an expensive outgoing lamp, thereby reducing running costs.

(6) An excellent solar cell can be provided by forming a metal memberconsisting of at least one of gold, silver, copper, stainless steel, andaluminum as a main component. The metal member from which electric powergenerated by the photovoltaic element is externally obtained mustcomprise a conductive material that minimizes output losses and has ahigh weather resistance, for example, long-term stability. A highlyconductive photovoltaic element module with few resistance losses can beprovided by using gold, silver, copper, stainless steel, or aluminum. Inparticular, stainless steel can be used to provide a relativelyinexpensive rust and a weather resistant photovoltaic element module.

(7) The method of providing a medium capable of absorbing 10% or more oflaser light having a wavelength of 0.4 μm to 2.0 μm on the surface ofthe metal member can include either employing as a medium a part of themetal member used for the photovoltaic element, or supplementallysupplying a medium during the production step. A method wherein a partof the metal member is used as the medium includes treating the metalmember in a strong-acid solution to oxidize or etch its surface, platingthe surface of the metal member, and coating the surface of the metalmember with carbon black. In addition, the method of supplementallysupplying the medium during the production step includes closelycontacting a material of a low surface reflectance with the surface ofthe metal member and irradiating the metal member with laser light froma low surface reflectance side of the material to weld the metal memberwith the material that has low surface reflectance. After welding, thematerial is preferably removed, but may not be removed depending on thematerial.

(8) When the medium capable of absorbing light is a color ink providedon the surface of the metal member, the process of applying the ink isvery simple. The color ink can be applied by either a felt pen, jetting,or silk screen printing. Even when a highly reflective metal is used, acolor ink can be provided on the surface of the metal to allow laserlight to be easily introduced into the metal, thereby providing a stablewelding strength to form a very reliable photovoltaic element module.

(9) The most stable welding strength can be obtained when the mediumcapable of absorbing laser light, which is provided on the surface ofthe metal member, is a film having a thickness bf 5 μm to 30 μm. Basedon the film characteristics, the film material is selected to match thewavelength of laser light used and is advantageous in controllingquality, such as thickness. In addition, when the metal member isirradiated with laser light from the film side to weld the metal memberwith the film, the film can be easily peeled off after welding when thethickness of the film is from 5 μm to 30 μm.

(10) When the medium capable of absorbing laser light, which is providedon the surface of the metal member, consists of at least Fe, Ni, orsolder, the welding strength can be stabilized, and the number ofoperations can also be reduced by plating Fe, Ni, or solder on thesurface of the metal member. The material for the metal member fromwhich electric power generated by the photovoltaic element is externallyobtained must be conductive to minimize output losses. It must also beweather resistant, having such characteristics as long-term stability.Therefore, a material plated with Fe, Ni, or solder is preferably usedwhen the metal member comprises, for example, copper.

The non-contact treatment of the present invention is an improvednon-contact treatment using, for example, laser or halogen light to cutor weld a high-reflection material, such as gold, silver, copper, oraluminum that is often used for electric parts, such as photovoltaicelements. In addition to the effects described in the above (1) to (6),this method has the following effects.

(11) The present invention provides a non-contact treatment methodwherein energy is supplied from an energy supply means, comprisingplacing on a material to be treated a non-adhering medium capable ofabsorbing energy and irradiating the non-adhering medium with energy.This method can achieve stable non-contact treatment because thephysical characteristics of the placed medium determine the reflectanceand can enable high-speed treatment, because the non-adheringanti-reflection material can be removed after the non-contact treatment.

(12) When the surface of the non-adhering medium that closely contactsthe material to be treated has a surface roughness of 0.1 nm to 5,000 nmin mean square, more stable welding is possible and the non-adheringanti-reflection material can be easily removed. Beyond 5,000 nm, stabletreatment is impossible, because the medium does not closely contact thematerial, whereby energy is not efficiently introduced to the inside ofthe material to be treated. In addition, below 0.1 nm the non-adheringmedium sticks significantly to the material during energy irradiation,whereby the medium is not easily removed after the treatment.

(13) When the non-adhering medium has at least a polymer film, that is,when it is, for example, a polyethyleneterephthalate film mixed withcarbon black, a polyethylenenaphthalate film with carbon black coated ordeposited on its surface, or a material with a stainless steel foillaminated thereon, it can be removed more easily after energyirradiation because the above material is very strong and thin andbecause the polymer film is dissolved and volatilized during energyirradiation. In addition, polymer films are supplied in a long sizeenough to easily enable mass production.

(14) The effect of the present invention can be most effectivelyobserved when the non-adhering medium is a magnetic tape. The magnetictape is excellent in stable workability, mold-releasing capability, andhigh-speed treatment. The mold-releasing capability can be improved byclosely contacting the surface of the magnetic tape with the material tobe treated.

(15) An object of the present treatment method is to efficiently guideenergy to the material to be treated. Particularly suitable energy islight, heat, or electromagnetic waves.

(16) The anti-reflection material (non-adhering medium) is irradiatedwith energy, while the non-adhering medium is holding the material to betreated, whereby the medium and the material are in close contact witheach other to stabilize treatment.

(17) Since the non-adhering medium is removed by energy irradiationand/or after the non-contact treatment, the non-adhering medium does notremain in the treated part after the non-contact treatment, therebypreventing post-process appearance and defect problems.

(18) When the non-adhering medium is supplied from the form of a roll,which is wound up after energy irradiation, it can be continuouslysupplied to enable mass production and to increase treatment speed.

(19) An object of the present invention is to achieve a stablenon-contact treatment, which is particularly suitable for welding orcutting.

(20) When the material to be treated is an electrode, it can be joinedstably and reliably. In particular, when the material to be treated isan electrode for a photovoltaic element, the non-adhering andanti-reflection medium does not remains on the electrode portion,improving the appearance while avoiding the need to account for thecompatibility with a package material.

Examples of the present invention are described below.

EXAMPLE 1

FIGS. 1A to 2C are schematic views showing the appearance of aphotovoltaic element module according to Example 1 of the presentinvention. FIG. 1A is a plan view of a photovoltaic element as seen fromits light-receiving surface, and FIG. 1B is a sectional view of thephotovoltaic element shown in FIG. 1A, which is taken along line 1B—1Bin FIG. 1A. In addition, FIG. 2A is a plan view of two photovoltaicelements connected in series as seen from their light-receiving surface,FIG. 2B is an enlarged view of the series-connected portion in FIG. 2A,and FIG. 2C is a sectional view of FIG. 2B.

In FIG. 1A, reference numeral 100 indicates a 300 mm×280 mm photovoltaicelement comprising a substrate 102, a lower electrode layer 103, asemiconductor layer 104 consisting of amorphous silicon and having aphotovoltaic function, and an upper electrode layer 105.

In this example, the substrate 102 for supporting the entirephotovoltaic element comprises a stainless steel plate having athickness of 150 μm. An Al layer about 2,000 Å thick and a ZnO layerabout 13,000 Å thick were sequentially formed on the substrate 102 asthe lower electrode layer 103 by a sputtering method. In addition, thesemiconductor layer 104 was formed by sequentially stacking an n-, i-,p-, n-, i-, and p-type semiconductor layers this order from thesubstrate side by a plasma CVD method. The thickness of these layers wasabout 150 Å, 4,000 Å, 100 Å, 100 Å, 800 Å, and 100 Å, respectively. Inaddition, the upper electrode layer 105 was a transparent electrodeconsisting of a thin indium oxide film about 700 Å thick, formed bydepositing In in an O₂ atmosphere using the resistance heating method.Furthermore, to prevent an effective light-receiving area from beingaffected by the adverse effect of a short circuit between the substrateand the transparent electrode that may occur when the outercircumference of the photovoltaic element is cut, etching pastecontaining FeCl₃, or AlCl₃ was coated on a part of the upper electrodelayer 105 by using screen printing, and was heated and washed tolinearly remove the part of the upper electrode layer 105 in order toform an etching line 101.

Subsequently, a copper foil strip 10 mm wide, 285 mm long, and 100 μmthick was formed near one side (280 mm long) of the back surface (on thesubstrate 102 side) of the photovoltaic element as a rear-surface-sideconductive foil 109, using the method described in Japanese PatentApplication Laid-Open No. 8-139349. One side of the copper foil stripprotruded out from the photovoltaic element 100, as shown in FIG. 1A.

Subsequently, an insulating adhesive tape 108 comprising a polyimide asa base and having a width of 10 mm, a length of 280 mm, and a thicknessof 50 μm was applied to one side of the front surface (upper electrodelayer 105 side) of the photovoltaic element so that the tape 108 wasopposed to the back-surface-side conductive foil 109.

Subsequently, a carbon-coating wire comprising a copper wire 100 μm indiameter and coated with a carbon paste was formed on the front sidesurface of the photovoltaic element as a collecting electrode 106. Inthis case, the carbon-coating wires were continuously formed on theupper electrode layer 105 and the insulating adhesive tape 108 at apitch of 14 mm in such a manner, that the wires crossed the insulatingtape.

Furthermore, a front-surface-side conductive foil 107 that is a furthercollecting electrode different from the collecting electrode 106, wasformed on the insulating adhesive tape 108. The front-surface-sideconductive foil 107 was formed by first placing a copper foil strip thatwas 20 mm wide, 285 mm long, and 100 μm thick on the insulating adhesivetape 108, with a part of the collecting electrode 106 interposedtherebetween, and then heating, pressurizing and fixing the strip at200° C. and 3 kg/cm² for 180 seconds. One side of the copper foil stripprotruded out from the photovoltaic element 100 at a side opposite tothe back-surface-side conductive foil 109, as shown in FIG. 1A.

To use the photovoltaic element produced in this manner for electricpower generation, a plurality of photovoltaic elements were electricallyconnected in series to produce a photovoltaic element module. Theconnection method is described in FIGS. 2A to 2C.

As shown in FIGS. 2A to 2C, two adjacent photovoltaic elements werearranged in such a way, that a part of the front-surface-side conductivefoil 107 of a photovoltaic element 1 overlapped a part of theback-surface-side conductive foil 109 of a photovoltaic element 2 over adistance of 3 mm.

Then, the overlapping portion between the front-surface-side conductivefoil 107 of the photovoltaic element 1, the back-surface-side conductivefoil 109 of the photovoltaic element 2 was irradiated with laser lightto be welded, thereby mechanically and electrically connecting the twoelements. Reference numeral 110 is a welding point. The laser forproviding a sufficiently high power to weld a metal preferably has awavelength of 0.4 μm and more. A solid laser having a wavelength of 0.4μm to 2.0 μm is particularly preferable. Applicable lasers include a YAGlaser, a phosphate glass laser, a silicate glass laser, and a CO₂ laser.In this example, a YAG laser (wavelength: 1.06 μm) was used to carry outthe welding under the following conditions: outgoing energy: 15.0J;pulse width: 5.0 ms; welding point diameter: 0.5 mm; number of weldingpoints: 6.

Subsequently, the electric resistance of the laser welded portion wasmeasured at 0.013 Ω. With respect to the performance of the photovoltaicelement 100, the effective area was 809.0 cm², the generated currentdensity was 5.38 A, the generated current was 5.38 A, the generatedvoltage was 1.2 V, and the generated electric power was 6.45 W.Therefore, the resistance loss of the laser welded portion was 0.9 mW.This corresponds only to 0.015% of the electric power generated by thephotovoltaic element 100.

In addition, the tensile strength of the laser welded portion wasmeasured to be in a range of 8 kg to 15 kg.

In this example, with respect to the time required for laser welding,2.0 seconds were required for feed-in and positioning the photovoltaicelements 1 and 2, 3.5 seconds were required for welding (including themovement of the laser beam outgoing tip), and 1.0 second was requiredfor feed-out of the elements. Thus, the connection of two photovoltaicelements was completed in 6.5 seconds.

That is, this example can provide a reliable series-connectedphotovoltaic element module that is produced at a speed higher than thatof conventional examples, as well as a method of producing it.

EXAMPLE 2

FIGS. 3A to 4C are schematic views showing the appearance of aphotovoltaic element module according to Example 2 of the presentinvention. FIG. 3A is a plan view of a photovoltaic element as seen fromits light-receiving surface, and FIG. 3B is a sectional view of thephotovoltaic element shown in FIG. 3A, which is taken along the line3B—3B in FIG. 3A. In addition, FIG. 4A is a plan view of twophotovoltaic elements connected in series as seen from theirlight-receiving surface, FIG. 4B is an enlarged view of theseries-connected portion in FIG. 4A, and FIG. 4C is a sectional view ofFIG. 4B.

In this example, a material was previously plated with Ni on a portionto be irradiated with laser light. The Ni plating was used as a mediumcapable of absorbing light.

In FIG. 3A, reference numeral 200 indicates a 300 mm×280 mm photovoltaicelement comprising a substrate 202, a lower electrode layer 203, asemiconductor layer 204 consisting of amorphous silicon and having aphotovoltaic function, and an upper electrode layer 205. Referencenumeral 201 designates an etching line, 206 a collecting electrode, 207a front-surface-side conductive foil that is a further collectingelectrode different from the collecting electrode 206, 208 an insulatingadhesive tape, and 209 a back-surface-side conductive foil. Thesecomponents were formed of the same materials as in Example 1 by usingthe same method as in Example 1. The front-surface-side conductive foil207 and the rear-surface-side conductive foil 209 were formed not toprotrude out from the photovoltaic element 200.

A plurality of the above photovoltaic elements were electricallyconnected in series. The connection method is described with referenceto FIGS. 4A to 4C. In this example, a connection member 211 was employedfor connections. First, the metal member 211, which is the connectionmember, was arranged to be in contact with the photovoltaic elements 1and 2, as shown in FIG. 4C. Then, the metal member was irradiated withYAG laser light (indicated by the arrows in FIG. 4C) in the same manneras in Example 1, except the output energy was 6.0J. Reference numeral210 denotes a welding point. The metal member 211 comprised anickel-plated copper material (width: 10 mm; length: 275 mm; thickness:100 μm), consisting of an inexpensive and conductive copper materialplated with a 2 μm thick nickel-containing material that absorbs about50% of YAG laser light having a wavelength of 1.06 μm. Since nickelabsorbs YAG laser light much better than copper (that is, nickel hasfewer losses caused by reflection from the surface of the metal), theoutput energy of the YAG laser could be reduced. In this example, theoutput energy from the YAG laser was 6.0J, but good welding results asin Example 1 could still be obtained.

Although, in this example, the medium capable of absorbing light wasprovided by plating the metal material (copper material) with nickel,the effects shown in FIG. 15 as described above could be obtained usinga metal member coated with carbon black was used.

That is, this example can provide a reliable series-connectedphotovoltaic element module that costs less than Example 1 and thatoperates faster than the conventional examples, as well as its producingmethod.

EXAMPLE 3

FIGS. 5A and 5B and 6A to 6C are schematic views showing the appearanceof a photovoltaic element module according to Example 3 of the presentinvention. FIG. 5A is a plan view of a photovoltaic element as seen fromits light-receiving surface, and FIG. 5B is a sectional view of thephotovoltaic element shown in FIG. 5A, which is taken along the line5B—5B in FIG. 5A. In addition, FIG. 6A is a plan view of twophotovoltaic elements connected in series as seen from theirlight-receiving surface, FIG. 6B is an enlarged view of theseries-connected portion in FIG. 6A, and FIG. 6C is a sectional view ofFIG. 6B.

In this example, a portion to be irradiated with laser light waspreviously coated with a color ink as a medium capable of absorbinglight.

In FIG. 5A, reference numeral 300 indicates a 300 mm×280 mm photovoltaicelement comprising a substrate 302, a lower electrode layer 303, asemiconductor layer 304 consisting of amorphous silicon and having aphotovoltaic function, and an upper electrode layer 305. Referencenumeral 301 designates an etching line, 306 a collecting electrode, 307a front-surface-side conductive foil that is a further collectingelectrode different from the collecting electrode 306, 308 an insulatingadhesive tape, and 309 a back-surface-side conductive foil. Thesecomponents were formed of the same materials as in Example 1 by usingthe same method as in Example 1.

A plurality of the above photovoltaic elements were electricallyconnected in series. The connection method is described with referenceto FIGS. 6A to 6C.

As shown in FIGS. 6A to 6C, two adjacent photovoltaic elements werearranged in such a way that a part of the front-surface-side conductivefoil 307 of the photovoltaic element 1 and a part of theback-surface-side conductive foil 309 of the photovoltaic element 2overlapped over a distance of 3 mm.

Then, a blue felt pen (Oily Magic ink No. 500) was used to coat a colorink 313 (having an absorptivity of 30% at a wavelength of 1.06 um) as amedium capable of absorbing light on the overlapping portion of thefront-surface-side conductive foil 307 of the photovoltaic element 1.Welding points 310 in the area coated with the color ink 313 wereirradiated with a YAG laser under the same conditions as in Example 2 tomechanically and electrically connect the two conductive foils. Forexample, a solid laser having a wavelength of 0.4 μm to 2.0 μm may beused instead of the YAG laser.

This example produced good results, similar to those in Example 2.

Similar results were obtained by using a color ink having anabsorptivity of 10% (a sky blue felt pen) instead of the color ink 313.In addition, similar results were obtained by using ink jet or silkscreen printing instead of a felt pen.

EXAMPLE 4

FIGS. 7A and 7B and 8A to 8C are schematic views showing the appearanceof a photovoltaic element module according to Example 4 of the presentinvention. FIG. 7A is a plan view of a photovoltaic element as seen fromits light-receiving surface, and FIG. 7B is a sectional view of thephotovoltaic element shown in FIG. 7A, which is taken along the line7B—7B in FIG. 7A. In addition, FIG. 8A is a top view of two photovoltaicelements connected in parallel as seen from their light-receivingsurface, FIG. 8B is an enlarged view of the series-connected portion inFIG. 8A, and FIG. 8C is a sectional view of FIG. 8B.

In this example, metal substrates were connected in parallel by laserwelding. In FIG. 7A, reference numeral 400 indicates a 300 mm×280 mmphotovoltaic element comprising a substrate 402, a lower electrode layer403, a semiconductor layer 404 consisting of amorphous silicon andhaving a photovoltaic function, and an upper electrode layer 405.Reference numeral 401 designates an etching line, 406 a collectingelectrode, 407 a front-surface-side conductive foil that is a furthercollecting electrode different from the collecting electrode 406, 408 isan insulating adhesive tape. These components were formed of the samematerials as in Example 1 by using the same method as in Example 1.Since, however, the metal substrate 402 was used as a back-surface-sideterminal, the back-surface-side conductive foil was not provided. Inaddition, the front-surface-side conductive foil 407 was formed notprotrude out from the photovoltaic element 400.

A plurality of photovoltaic elements were electrically connected inparallel. The connection method is described with reference to FIGS. 8Ato 8C.

As shown in FIGS. 8A to 8C, two adjacent photovoltaic elements werearranged in such a way that the substrate 400 of the photovoltaicelement 1 and the substrate 400 of the photovoltaic element 2 were inclose contact. The closely contacting portion between the two substrateswas irradiated with YAG laser light to weld and connect them to eachother. Although this example used the YAG laser, one of the other lasersdescribed above may be employed. Since this example used stainless steelmainly consisting of Fe (having an absorptivity of about 30% at awavelength of 1.06 μm) as the substrate 400, stable welding could beachieved while applying low energy.

Subsequently, a metal member 411, which also functioned as a connectionmember, was placed to contact the front-surface-side conductive foils407 of the photovoltaic elements 1 and 2, and the metal member 411 wasirradiated with YAG laser light to weld the elements together in orderto connect them in parallel. Reference numeral 410 indicates a weldingpoint. The metal member 411 was similar to the metal member 211 and thewelding conditions were similar to these in Example 2.

The present invention enables both the front and back sides to be stablywelded at low cost and provides a parallel-connected photovoltaicelement module having excellent connection stability, as well as amethod of producing it.

EXAMPLE 5

FIGS. 9A to 10C are schematic views showing the appearance of aphotovoltaic element module according to Example 5 of the presentinvention. FIG. 9A is a plan view of a photovoltaic element as seen fromits light-receiving surface, and FIG. 9B is a sectional view of thephotovoltaic element shown in FIG. 9A, which is taken along the line9B—9B in FIG. 9A. In addition, FIG. 10A is a plan view of twophotovoltaic elements connected in series as seen from theirlight-receiving surface, FIG. 10B is an enlarged view of theseries-connected portion in FIG. 10A, and FIG. 10C is a sectional viewof FIG. 10B.

In this example, a film was previously arranged on a portion to beirradiated with laser light, as a medium capable of absorbing light.

In FIG. 9A, reference numeral 500 indicates a 300 mm×280 mm photovoltaicelement comprising a substrate 502, a lower electrode layer 503, asemiconductor layer 504 consisting of amorphous silicon and having aphotovoltaic function, and an upper electrode layer 505. Referencenumeral 501 designates an etching line, 506 a collecting electrode, 507a front-surface-side conductive foil that is a further collectingelectrode different from the collecting electrode 506, 508 an insulatingadhesive tape, and 509 a back-surface-side conductive foil. Thesecomponents were formed of the same materials as in Example 1 by usingthe same method as in Example 1. The back-surface-side conductive foil509 was formed not to protrude out from the photovoltaic element 500.The front-surface-side foil 507 was 10 mm wide, 285 mm long, and 100 μmthick, and one side of the foil 507 extended outward from thephotovoltaic element 500.

A plurality of photovoltaic elements were electrically connected inseries. The connection method is described with reference to FIGS. 10Ato 10C.

As shown in FIGS. 10A to 10C, two adjacent photovoltaic elements werearranged in such a way, that a part of the front-surface-side conductivefoil 507 of the photovoltaic element 1 and a part of theback-surface-side conductive foil 509 of the photovoltaic element 2overlapped over a distance of 3 mm. In this case, the interval betweenthe photovoltaic elements 1 and 2 was 2 mm.

A film 513 was arranged as a medium capable of absorbing light on theoverlapping portion between the front-surface-side conductive foil 507of the photovoltaic element 1 and the back-surface-side conductive foil509 of the photovoltaic element 2. This example used a black PET(polyethylene-terephthalate) tape (MELINEX 427, produced by ICI JapanLtd.; absorptivity at a wavelength of 1.06 μm: 65%; thickness: 20 μm;width: 13 mm) was used as the film 513. Welding points (not shown in thedrawings) on the surface of the film 513 were irradiated with YAG laserlight as shown by the arrows in FIG. 10C to mechanically andelectrically connect two conductive foils. For example, a solid laserhaving a wavelength of 0.4 μm to 2.0 μm may be used instead of the YAGlaser.

This example provided good results, similar to those obtained in Example2.

When a film is used as the medium, as in this example, a film having athickness of 5 μm to 30 μm is preferable because this film can be easilyremoved after welding. When the thickness of the film is less than 5 μm,the film is likely to be torn off while being peeled off. In addition,when the thickness of the film is greater than 30 μm, the adhesionstrength of the film becomes excessively high, as shown in FIG. 16,thereby requiring a strong force to peel off the film. As a result, thewelded metal member may be deformed or the film may be torn off. In FIG.16, symbol (1) designates LUMIRROR X (produced by Toray Industries,Inc.), symbol (2) denotes MELINEX 427 (produced by ICI Japan Ltd.), orsymbol (3) indicates OPP silicon (produced by Panac Co., Ltd.). FIG. 16shows the results obtained when used the films (1), (2) and (3). Such anincrease in adhesion strength is caused by the adhesion of the film basematerial (medium) melted by laser light of a constant diameter to themetal member. This does not present a problem when the film basematerial is so thin that only a small amount of the base material melts.However, a problem arises when the thickness of the film base materialis greater than a certain value, and the melted amount of the basematerial and the adhesion strength exhibit a positive correlation.

The present invention is not limited to the above examples.

EXAMPLE 6

According to this example, an aluminum sheet that constituted anelectrode for an electric part was cut. FIG. 17 is a schematic viewshowing a laser treatment method according to Example 6 of the presentinvention.

In FIG. 17, reference numeral 800 indicates the irradiation of CO₂ laserexcited infrared light, and reference numeral 801 indicates anon-adhering medium consisting of black polyethyleneterephthalate film10 mm wide, 13 cm long, and 0.3 mm thick. Although this example used aMELINEX 427 film produced by ICI Japan Ltd. as the non-adhering medium801, the experiments conducted by the inventors confirmed thatperformance similar to that of this example could be obtained when usedLUMIRROR X30 produced by Toray Industries, Inc. The surface roughness ofthe nonadhering medium 801 was measured to be in a range of 0.1 nm to 2nm in mean square, by using a three-dimensional surface roughness meterof a non-contact optical system. In addition, reference numeral 802indicates a material to be treated consisting of an aluminum sheethaving a length of 10 cm and a thickness of 0.5 mm.

The material 802 was fixed to a jig (not shown in the drawings) having agroove formed at a laser irradiation position, and a non-adhering medium801 was placed on the material 802 at a position to be irradiated withlaser light. Subsequently, a presser jig (not shown in the drawings),having a groove to be penetrated by laser light at a cutting position,was used to closely contact the non-adhering medium 801 with thematerial 802 at 1 kg/cm² pressure. Subsequently, using Ar as a shieldgas, the material to be treated was irradiated with laser light 800along the groove to be penetrated by the light to cut the material 802.The irradiation conditions of the laser light 800 were as follows:outgoing energy: 251; pulse width: 3 ms; pulse repetition speed: 15 PPS;laser beam diameter: φ0.5 mm.

The laser irradiated portion of the non-adhering medium 801 was meltedand evaporated by the irradiation of laser light. Once cutting wascompleted, the presser jig was opened and the remaining non-adheringmedium 801 was removed by using tweezers to complete the series ofoperations. Although in this example the tweezers are used to remove thenon-adhering medium 801, a method of blowing the medium off by a shieldgas may be suitably used.

Since in this example the non-adhering medium 801 was placed on thelaser light-irradiated surface of the material to be treated, the amountof energy required for cutting could be substantially reduced.Furthermore, since the non-adhering medium 801 is removed after laserirradiation, the non-adhering medium 801 does not remain after theseries of operations have been finished, thereby avoiding appearanceproblems and preventing problems from occurring in the post-process.

This example teaches a stable laser treatment, because the treatment canbe carried out at a lower energy than the conventional techniques andthe reflectance is determined by the physical characteristics of theplaced non-adhering medium. In addition, the material is treated whileholding the non-adhering medium, thereby enabling stable close contactand, thus, a stable laser treatment. Furthermore, the operator needsonly to place the non-adhering medium, thereby increasing the treatmentspeed. In addition, since the nonadhering medium can be easily removedafter laser treatment, the present example provides a laser treatmentmethod that avoids appearance problems, while also preventing problemsin the post-process.

EXAMPLE 7

In this example, laser light was used to weld the electrodes ofphotovoltaic elements. The electrodes consisted of a copper foil.

FIGS. 18A and 18B and 19A to 19C are schematic views showing theappearance of a photovoltaic element module according to Example 7 ofthe present invention. FIG. 18A is a plan view of a photovoltaic elementas seen from its light-receiving surface, and FIG. 18B is a sectionalview of the photovoltaic element shown in FIG. 18A, which is taken alongthe line 18B—18B in FIG. 18A. In addition, FIG. 19A is a plan view oftwo photovoltaic elements connected in series as seen from theirlight-receiving surface, FIG. 19B is an enlarged view of theseries-connected portion in FIG. 19A, and FIG. 19C is a sectional viewof FIG. 19B. FIG. 20 is a schematic view showing the method of supplyingnon-adhering and anti-reflection materials according to Example 7.

In FIG. 18A, reference numeral 900 indicates a 300 mm×280 mmphotovoltaic element comprising a substrate 902, a lower electrode layer903, a semiconductor layer 904 consisting of amorphous silicon andhaving a photovoltaic function, and an upper electrode layer 905.

In this example, the substrate for supporting the entire photovoltaicelement comprises a 150 μm thick stainless steel plate. An Al layerabout 2,000 Å thick and a ZnO layer about 13,000 Å thick weresequentially formed on the substrate 902 as the lower electrode layer903 by using the sputtering method. In addition, the semiconductor layer904 was formed by sequentially stacking an n-, i-, p-, n-, i-, andp-type semiconductor layers in this order from the substrate side byusing the plasma CVD method. The thicknesses of these layers were about150 Å, 4,000 Å, 100 Å, 100 Å, 800 Å, and 100 Å, respectively. Inaddition, the upper electrode layer 905 was a transparent electrodeconsisting of a thin indium oxide film of about 700 Å in thickness, andwas formed by depositing In in an O₂ atmosphere by using the resistanceheating method. Furthermore, to prevent an effective light-receivingarea from being affected by the adverse effect of a short circuitbetween the substrate and the transparent electrode that may occur whenthe outer circumference of the photovoltaic element is cut, etchingpaste containing FeCl₃ or AlCl₃ was coated on a part of the upperelectrode layer 905 by using screen printing, and was heated and washedto linearly remove the part of the upper electrode layer 905 to therebyform an etching line 901.

Subsequently, a copper foil strip having a width of 10 mm, a length of285 mm, and a thickness of 100 μm was formed near one side (280 mm long)of the back surface (on the substrate 902 side) of the photovoltaicelement as a back-surface-side conductive foil 909, by using the methoddisclosed in Japanese Patent Application Laid Open No. 8-139349. Oneside of the copper foil strip protruded out from the photovoltaicelement, as shown in FIG. 18A.

Subsequently, an insulating adhesive tape 908 comprising polyimide as abase and having a width of 10 mm, a length of 280 mm, and a thickness of50 μm was applied to one side of the front surface (on the upperelectrode layer 905) of the photovoltaic element such that the tape 908is opposed to the back-surface-side conductive foil 909.

Subsequently, a carbon-coating wire comprising a copper wire 100 μm indiameter and coated with carbon paste was formed on the front surface ofthe photovoltaic element as a collecting electrode 906. In this case,the carbon-coating wires were continuously formed on the upper electrodelayer 905 and the insulating adhesive tape 908 at a pitch of 14 mm suchthat the wires crossed the insulating tape.

Furthermore, a front-surface-side conductive foil 907 that was a furthercollecting electrode different from the collecting electrode 906 wasformed on the insulating adhesive tape 908. The front-surface-sideconductive foil 907 was formed by placing a copper foil strip having awidth of 10 mm, a length of 285 mm, and a thickness of 100 μm on theinsulating adhesive tape 908 with interposition of a part of thecollecting electrode 906 therebetween and heating, pressurizing, fixingthe strip at 200° C. and 1 kg/cm² for 60 seconds. One side of the copperfoil strip was protruded out from the photovoltaic element 900 on a sideopposite to the back-surface-side conductive foil 909, as shown in FIG.18A.

To use the photovoltaic element produced in this manner for electricpower generation, a plurality of photovoltaic elements were electricallyconnected in series to produce a photovoltaic element module. Theconnection method is described in FIGS. 19A to 19C.

As shown in FIGS. 19A to 19C, two adjacent photovoltaic elements werearranged so that a part of the front-surface-side conductive foil 907 ofa photovoltaic element 1 overlapped a part of the back-surface-sideconductive foil 909 of a photovoltaic element 2 over a distance of 3 mm.

Subsequently, a non-adhering medium 913 was placed on the overlappinglaser-welded portion between a part of the front-surface-side conductivefoil 907 of the photovoltaic element 1 and a part of theback-surface-side conductive foil 909 of the photovoltaic element 2. Asthe non-adhering medium 913, a commercially available magnetic tape wasused, which comprises a magnetic substance, such as carbon black, coatedor deposited on one side of polyethyleneterephthalate orpolyethylenenaphthalate. This example used T-120VF produced by SonyCorporation, but the experiments conducted by the inventors confirmedthat performance similar to that of this example can be obtained whenused other magnetic tapes, such as P6-120HMP2 or VXST-120VF, produced bySony Corporation, or NV-ST120XPZ or NV-TTC40HGK produced by MatsushitaElectric Industrial Co., Ltd., or heat transfer ribbons, such as TL-12Kproduced by King Jim Co., Ltd., CF-PR190 produced by Matsushita ElectricIndustrial Co., Ltd., or JW-Z180 produced by Toshiba Corporation. Sincethese magnetic tapes are supplied in a form of a roll, a subsequentlaser treatment can be prepared by releasing the presser jig and feedingthe tape forward after each laser treatment. In addition, the surfaceroughness of the magnetic surfaces of these magnetic tapes was measuredto be in a range of 5 nm to 20 nm in mean square.

Furthermore, a presser jig (not shown in the drawings) was used to pressthe magnetic tape that was the non-adhering medium 913 at 10 kg/cm² withthe magnetic surface facing the front-surface-side conductive foil 907of the photovoltaic element 1, which was a material to be treated.

Then, the overlapping portion between the front-surface-side conductivefoil 907 of the photovoltaic element 1 and the back-surface-sideconductive foil 909 of the photovoltaic element 2, which was pressed bythe presser jig, was irradiated with laser light to carry out weldingand mechanically and electrically connect the elements to each other.Reference numeral 910 designates a welding point. As the laser forproviding a high energy enough to weld a metal, it is possible to use aYAG laser, a phosphate glass laser, a silicate glass laser, or aCO₂-laser-excited far infrared laser. In particular, the YAG laser hasexcellent characteristics, such as its capability of transmitting laserlight through optical fibers to enable treatment at a position remotefrom the laser oscillator, and enables the welding condition to bechanged by the selection of the optical fibers and an outgoing unit.Another excellent characteristic of this laser is its capability ofdividing a laser light into 2 to about 10 beams.

In this example the YAG laser was used to execute welding under thefollowing conditions: outgoing energy: 6J; pulse width: 5 ms; laserdiameter: 0.6 mm; number of welding points: 12.

The method of supplying the magnetic tape as the non-adhering medium 913according to this example is described with reference to FIG. 20. Inthis figure, reference numeral 920 indicates a magnetic tape housed in acassette, 921 a reel around which a magnetic tape irradiated with laserlight is wound, and 922 a presser member for pressing the magnetic tape913 against a junction portion between the front-surface-side conductivefoil 907 of the photovoltaic element 1 and the back-surface-sideconductive foil 909 of the photovoltaic element 2, which are materialsto be treated. A transfer means (not shown in the drawings) is used totransfer to a laser treatment position the front-surface-side andback-surface-side conductive foils 907 and 909 of the photovoltaicelements 1 and 2, respectively. Then, the presser jig 922 presses themagnetic tape 913 against the junction portion between thefront-surface-side conductive foil 907 of the photovoltaic element 1 andthe back-surface-side conductive foil 909 of the photovoltaic element 2.Subsequently, the junction portion is irradiated with laser light 930 tocarry out a predetermined laser treatment.

The portion of the magnetic tape 913 irradiated with laser light meltsand is evaporated by the heat generated by welding. Furthermore, since amagnetic substance having a surface roughness of 5 nm to 20 nm in meansquare is coated or deposited on the surface of the magnetic tape 913closely contacting the front-surface-side conductive foil 907 of thephotovoltaic element 1, after welding, the magnetic tape 913 can beremoved by simply releasing the presser jig. The magnetic tape 913 mayadhere to the front-surface-side conductive foil 907 in some cases, butcan be easily removed by applying force to slightly release the tapefrom the foil (not shown in the drawings).

Subsequently, the magnetic tape 913 is fed by 3 cm to be wound aroundthe winding reel 921, and an unused magnetic tape is supplied from themagnetic tape cassette 920 to complete preparations for the subsequentlaser treatment. The treated photovoltaic elements 1 and 2 are conveyedout by a transfer means (not shown in the drawings) immediately afterlaser treatment.

The electric resistance of the laser welded portion was measured to be0.013 Ω. With respect to the performance of the photovoltaic element900, the effective area was 809.0 cm², the generated current was 5.38 A,the generated voltage was 1.2 V, and the generated power was 6.45 W,therefore the resistance loss of the laser welded portion was 0.9 mW,which is only 0.015% of the generated electric power of 6.45 W.

In addition, the tensile strength of the laser welded portion wasmeasured to be in a range of 8 kg to 15 kg.

In this example, with respect to the time required for laser welding,2.0 seconds were required to feed-in and position the photovoltaicelements 1 and 2, 3.5 seconds were required for welding (including themovement of the laser beam outgoing tip), and 1.0 second was requiredfor feed-out of the treated elements. Thus, the connection of the twophotovoltaic elements was completed in 6.5 seconds.

That is, this example can provide a method of connecting photovoltaicelements in series that enables laser welding at a lower energy than theconventional techniques, enables high speed treatment, and avoidsappearance problems while preventing post-process problems.

The present invention minimizes the time required for heating whenexecuted to connect a group of photovoltaic elements, thereby preventingthe components of the photovoltaic elements, such as the semiconductorlayer and conductive adhesive, from being degraded by wide-rangingheating.

In addition, in the present invention, each operation can be completedin a short time to enable mass production.

Furthermore, the present invention eliminates the needs for solder toavoid reduction of the production yield due to solder residues and toavoid the adverse effect of remaining fluxes on a covering material.

In addition, the present invention teaches using color ink or film toeasily increase the laser absorption efficiency, thereby providing aninexpensive photovoltaic element production method having a highproduction efficiency.

Furthermore, in the method of placing the nonadhering medium on thesurface to be irradiated with laser light of the material to be treated,and irradiating the non-adhering medium with laser light while holdingthe non-adhering medium and the material, laser treatment can be stablyexecuted because the reflectance is determined depending on the physicalproperties of the placed material (non-adhering medium). In addition,the treatment can be carried out while holding the non-adhering mediumand the material to be treated, thereby enabling stable close contacttherebetween, and thus stable laser treatment. Moreover, high speedtreatment is possible because of placing only the non-adhering medium.

What is claimed is:
 1. A photovoltaic element module comprising at leasttwo photovoltaic elements electrically connected to each other, whereina medium is provided on only an electric connection portion of thephotovoltaic element, the medium absorbing at least 10% or more of alight having a wavelength of 0.4 μm to 2.0 μm, wherein metal memberselectrically connected to each other in the electric connection portionare provided on each of the photovoltaic elements and wherein theelectric connection portion comprises a first metal member, a secondmetal member and the medium in that order.
 2. A photovoltaic elementmodule according to claim 1, wherein the photovoltaic element has atleast a conductive substrate and a semiconductor layer.
 3. Aphotovoltaic element module according to claim 1, wherein the medium isa color ink.
 4. A photovoltaic element module according to claim 1,wherein the medium is a film having a thickness of 5 μm to 30 μm.
 5. Aphotovoltaic element module according to claim 1, wherein the mediumcomprises Fe, Ni, or solder.
 6. A photovoltaic element module accordingto claim 1, wherein the medium absorbs 10% or more of a laser lighthaving a wavelength of 1.06 μm.
 7. A photovoltaic element moduleaccording to claim 1, wherein the metal members comprise gold, silver,copper, stainless steel, or aluminum as a main component.